An apparatus, such as a paper sheet distinguishing apparatus and an image reading apparatus, includes an image sensor unit that optically reads and outputs an object to be read. In some of the image sensor units applied to the apparatuses, light guides shape light emitted by light sources into a line (shape the light into a line light source) to emit the light to the object to be read, a light condenser condenses the light from the object to be read, and an image sensor IC array photoelectrically converts the light. The light guides provided on the image sensor unit are generally long and thin rod-like members, and long and thin light emission surfaces that emit light toward the object to be read are provided on side surfaces of the light guides. The light guides are assembled to a housing (for example, a frame) of the image sensor unit such that the light emission surfaces face the object to be read. A configuration of assembling the light guides to the housing is disclosed in Patent Literature 1, wherein in an image sensor unit including a plurality of light guides, a plurality of supporting members are mounted on each of the light guides, and the supporting members are coupled to the housing. In addition, structures, such as elastic claws, engaged with the light guides may be provided integrally with the frame, and the structures may be used to assemble the light guides to the frame.
By the way, the intensity of light (amount of light) emitted from the image sensor unit to the object to be read is preferably uniform throughout the whole length in the longitudinal direction. It is also preferable that the tendency of the distribution of the intensity of light in the longitudinal direction not change even when the object to be read is displaced in the optical axis direction of the light condenser. In other words, it is preferable that the distribution in the longitudinal direction of the output from the image sensor unit be similar even when the distance between the object to be read and the image sensor unit is changed. However, when the supporting members include parts engaged so as to cover the surfaces of the light guides closer to the object to be read as described in Patent Literature 1, the intensity of light emitted to the object to be read may be locally changed by the parts, and the distribution in the longitudinal direction may be nonuniform. Furthermore, according to the configuration, the similarity of output of the image sensor unit may be broken when the distance between the object to be read and the image sensor unit is changed.
Particularly, in the configuration including a plurality of light guides (two in Patent Literature 1), the local change in the intensity of light caused by the supporting members becomes large when the positions in the longitudinal direction of the supporting members mounted on each light guide are the same in all of the light guides. Therefore, the extent of the nonuniformity in the distribution of the intensity of light in the longitudinal direction becomes large, and the breaking of the similarity of output becomes large when the distance between the object to be read and the image sensor unit is changed. Note that in the structure in which the structures engaged with the light guides are provided integrally with the frame, the same problems may occur depending on the positions of the structures.